BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser processing apparatus that forms a structure on a work piece by use of laser beam, and a laser processing method therefor. More particularly, the invention relates to a laser processing apparatus that performs micro processing effectively for micro-machines or complex material and complicated configurations, such as IC and hybrid IC devices, and also, relates to a laser processing method therefore.
2. Related Background Art
Conventionally, it has been practiced to use higher harmonic waves of excimer laser or YAG laser for the formation of a structure by means of laser micro processing.
However, for these processing methods, the maximum energy concentration of laser beam is at a level of 100 mega watts in terms of oscillating pluses. As a result, it is difficult to process a work piece formed by inorganic material. Under the circumstances, only sublimating ablation process is possible for a work piece mainly formed by organic material.
Thus, when micro processing is given to a work piece formed by inorganic material, lithographic process is adopted for the execution of a series of processes, such as resist coating, resist patterning exposure, resist development, etching that utilizes resist pattern, and resist ashing, for each individual material of different property, respectively, when processing a structure. The adoption of a processing method of the kind makes the processing steps complicated, leading to problems related to costs. Also, there is a problem that the investments in the production facilities tend to become enormous against the process tact time. In order to improve the situation thus encountered, the applicant hereof has proposed a sublimation processing in the specification of Japanese Patent Application Laid-Open No. 11-316760 and others, in which when a structure is formed by micro processing on a work piece formed by inorganic material, the laser beam oscillated from a laser oscillator, which outputs laser beam at a pulse emission time of 1 pico second or less, is converged and irradiated onto the work piece in a designated energy concentration. In this way, the temporal energy concentration is significantly increased, and the energy concentration of the emitted laser beam reaches a level of approximately 3 giga watts (here, among generally available laser oscillators on the market, there exists the one having the pulse emission time of 150 femto seconds or less with light energy per pulse being 500 micro joules or more).
Beside this, the applicant hereof has also proposed a laser processing method for the execution of sublimating ablation process that utilizes the characteristics of extremely short laser irradiation time, in which laser beam is not transformed to thermal energy but directly converted into the energy that cuts lattice coupling.
Nevertheless, the laser beam oscillated from the oscillator, which outputs laser beam at a pulse emission time of 1 pico second or less as described above, is generally the laser developed by reproducing amplification inductive emission of seed light. As a result, the diameter of the laser beam is as small as approximately Φ10 mm or less. Moreover, the transverse mode thereof is single, and it has coherent light with a high coherence. Therefore, unlike excimer laser, this laser beam cannot perform the collectively uniform irradiation of photo-mask pattern by use of an optical integrator, such as a homogenizer, due to such coherence. As a result, when an arrangement pattern should be processed, laser flux is allowed to pass a certain one pattern, and induced to irradiate a work piece with the step and repeat operation, which must be repeated. Also, when a continuous pattern should be processed, it may be possible to adopt a method whereby to process it by drawing a pattern by means of scanning of later beam. In this case, however, the control of etching depth depends on the overlapping of the scanning speed and the scanning position.
Under these circumstances, there is still a room for improvement with respect to the processing efficiency, such as to process a desired pattern collectively on a work piece in a short period of time by use of the laser beam oscillated from the laser oscillator that outputs laser beam at a pulse emission time of 1 pico second or less as described above. Now, among the laser oscillators that output laser beam at pulse emission time of 1 pico second or less, which are currently available on the market in general, there is the one the output of which reaches a level of approximately 3 giga watts. Therefore, the energy exerted by the laser beam emitted from such oscillator, which is necessarily applied to processing a work piece, is not even a half of the total energy of the laser beam emitted from such oscillator. The energy needed for processing is often several % thereof or less.
SUMMARY OF THE INVENTION
Here, therefore, the present invention is designed to aim at providing a laser processing apparatus capable of efficiently utilizing the energy, which is needed for processing, without generating any excessive energy when using the laser beam oscillated from the laser oscillator that outputs laser beam at pulse emission time of 1 pico second or less, hence implementing the enhancement of productivity with the increased processing efficiency, as well as to aim at providing a laser processing method therefor.
In order to achieve such aims, the laser processing apparatus of the present invention, which performs light ablation process using laser beam from a laser oscillator continuously emitting light pulse having large spatial and temporal energy concentration at pulse emission time of 1 pico second or less, comprises beam dividing means for dividing laser beam from the laser oscillator into plural beams, and optical systems provided separately for each of the divided beams. With the structure thus arranged, it is made possible for the laser processing apparatus to perform plural processing portions altogether by irradiating laser to plural processing portions at a time through the optical systems.
Also, the laser processing method of the invention for performing light ablation process, which uses laser beam from a laser oscillator continuously emitting light pulse having large spatial and temporal energy concentration at pulse emission time of 1 pico second or less, comprises the steps of dividing laser beam from the laser oscillator into plural beams; and processing plural processing portions altogether by irradiating laser to plural processing portions simultaneously through individual optical system per divided beam.
In accordance with the present invention, a structure is arranged to process by use of the laser beam oscillated from the laser oscillator that outputs laser beam at pulse emission time of 1 pico second or less, and laser beam is divided into plural beams for processing, and then, plural work pieces are irradiated by laser simultaneously through individual optical system per divided beam. In this manner, when laser processing is performed, excessive energy is not allowed to be generated, hence making it possible to effectively utilize energy needed for processing and implement the enhancement of productivity with such increased processing efficiency.
After that, each of the four laser beam fluxes is led to the photo-mask projection optical system shown in FIG. 2, respectively, thus processing a work piece 12. Here, the description will be made of the structure of the photo-mask projection optical system. In FIG. 2, one of the divided laser beams A, B, C and D is led in the direction indicated by an arrow in FIG. 2 to a zoom beam compressor 110 through a shutter 114 where it is converted into the one having a beam diameter of designated light. Then, it is further led to a mask illumination lens 111 to laser beam having a designated convergent angle for the illumination of the mask pattern portion of the photo-mask 11. At this juncture, depending on the compression ratio of the zoom beam compressor 110 and the focal length of the mask illumination lens 111, the effective NA (number of apertures), with which to process a work piece, is determined finally. In accordance with the NA thus determined, the processing shape of the work piece is determined. To describe this process the other way around, depending on the processing shape of a work piece, the compression ratio of the zoom beam compressor 110 and the focal length of the mask illumination lens 111 are determined or adjusted.